1. Field of the Invention
The present invention relates to a catalyst for polymerization and copolymerization of ethylene. More particularly, the invention relates to a solid titanium complex catalyst for polymerization and copolymerization of ethylene. Embodiments of the catalyst system include a solid titanium complex catalyst supported on a carrier containing magnesium. The catalyst may display high catalytic activity, excellent hydrogen reactivity during polymerization, and controlled particle size, whereby polymers of high bulk density may be produced.
2. Brief Description of the Related Art
The polymerization of ethylene is usually carried out in liquid phase in the presence of a solvent such as isopentane or hexane, or in the gas phase. The important factors affecting the polymerization in these processes are: polymerization activity and hydrogen reactivity of the catalyst, bulk density of the resulting polymers, the amount of monomers soluble in the solution, particle size distribution, and the existence of fine particles in the resulting polymers. Hydrogen reactivity may be generally defined as the extent of change in molecular weight of produced polymers in accordance with the amount of hydrogen which is used, during polymerization and copolymerization of ethylene, in order to control the molecular weight of the polymers. By using a catalyst having high hydrogen reactivity, the molecular weight of the polymers may be effectively controlled with small amounts of hydrogen, affording flexibility in the manipulation of the polymerization process.
Recently, many methods using titanium-based catalysts containing magnesium have been reported as a catalyst for polymerization and copolymerization of olefin. These catalysts may provide high catalytic activity and produce polymers of high bulk density, and are known to be suitable for liquid phase and gas phase polymerization.
For example, in using a magnesium solution to obtain a catalyst which may produce olefin polymers of high bulk density, the magnesium solution is prepared by reacting magnesium compounds with an electron donor. Electron donors include alcohols, amines, cyclic ethers, or organic carboxylic acids. The magnesium solution is prepared in the presence of a hydrocarbon solvent. A magnesium supported catalyst may be prepared by reacting the magnesium solution with halogen compounds such as titanium tetrachloride. Methods using an alcohol to prepare a magnesium solution are disclosed in U.S. Pat. Nos. 3,642,746, 4,336,360, 4,330,649, and 5,106,807. Also, U.S. Pat. Nos. 4,477,639 and 4,518,706 disclose a method which uses tetrahydrofuran or a cyclic ester as the solvent for dissolving the magnesium compound. Although these catalysts may produce polymers of high bulk density, the catalysts need to be improved regarding catalytic activity and hydrogen reactivity.
In addition, U.S. Pat. Nos. 4,847,227, 4,816,433, 4,829,037, 4,970,186, and 5,130,284 have reported the preparation of olefin polymerization catalysts which have good polymerization activity and can enhance the bulk density of resulting polymers. Increased polymerization activity was achieved by reacting electron donors such as magnesium alkoxyde, dialkylphthalate or phthaloyl chloride with a titanium chloride compound. U.S. Pat. No. 5,459,116 has reported a method for preparing a titanium solid catalyst by contacting a magnesium solution containing an ester having at least one hydroxyl group as an electron donor with a titanium compound. By this method, it is possible to obtain a catalyst which has high polymerization activity and affords high bulk density in resulting polymers, but there is much to be improved regarding hydrogen reactivity.
Finally, U.S. Pat. No. 5,869,418 discloses a method of enhancing hydrogen reactivity of a catalyst by using dialkoxyphenylalkane as an external electron donor during polymerization of propylene, and illustrates its advantage. The application of this method which uses an external electron donor in addition to a solid catalyst is, however, limited to the polymerization and copolymerization of propylene.
Therefore, there is a demand for catalysts for polymerization and copolymerization of ethylene which may be prepared by a simple process, have high polymerization activity and hydrogen reactivity. In addition, there is demand for catalysts which may produce polymers with narrow particle size distribution and small amount of fine particles.
The object of the present invention is to solve the problems of prior art methods as mentioned above, and to provide a catalyst for polymerization and copolymerization of ethylene. More particularly, the object is to proved a catalyst which has high catalytic activity as required in the polymerization and copolymerization of ethylene, controlled catalyst particle size to afford high bulk density to the resulting polymer, and high hydrogen reactivity to control the polymerization process easily.